Tim Henman's 2006 comeback campaign at the Qatar Open was cut short by Tommy Haas as the German swept past the British number one 6-2 7-6 in Doha. Haas broke the 31-year-old twice in the first set as a struggling Henman conceded a series of unforced errors.
Henman bravely clung on in the second set, saving seven match points to force the tie-break.
But a seventh ace from Haas was enough for him to claim the match and advance to the last eight.
Henman's serve had been solid in his first-round victory over third seed Richard Gasquet but against Haas it deserted him.
The Briton gifted the 28-year-old three set points at 5-2 in the opener and he meekly conceded with a double fault.
Haas continued to dictate the rhythm of the match from the baseline and Henman had to fight back at 5-4 down to hold on for the breaker.
The German hit the ball wide to give Henman a mini-break at 3-2 but a slice backhand at the net saw him level.
From then on it was Haas who held the momentum and he completed a competent victory with some stinging groundstrokes and two aces.
Henman said: "Of course I'm disappointed. I wasn't serving well while Tommy got his act together.
"You know how important the serves are in tennis, and I'm going to work on mine."
Haas, like Henman beset by injuries in 2005, said: "At times Tim came out to play big tennis. It was a tough task, but in the end I am happy."
He added: "My top priority is to stay healthy and fit. If I can, I am going to be the dangerous player on the Tour."
World number one Roger Federer, the defending champion, booked his quarter-final place with a hard-fought 7-6 (2) 7-6 (5) victory over France's Fabrice Santoro.
Switzerland's Federer next meets Marcos Baghdatis of Cyprus, who defeated eighth-seeded Spaniard Feliciano Lopez 6-1 3-6 7-5.
MMIX
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Tommy kept his composure which makes a change for him